单项选择题
A check line is（）.
A.a safety line attached to a man working over the side B.used to measure water depth C.used to slow the headway of a barge D.used to measure the overhead height of a bridge
单项选择题 A chock（）.
单项选择题 A chock is a（）.
单项选择题 A C02 portable extinguisher is annually checked by（）.
